It is the thought that counts. When it comes to a card, the gift is the thought. Every professor I know cherishes and shows off heartfelt cards from students. It might feel like a cop out on your part, but a card expressing your gratitude in writing will make your professor feel like his or her work counts. We all want to make a difference - your card will tell your professor that he or she has touched your life. It's an unbeatable gift.
Keep it Inexpensive
If you must present your professor with a gift other than a card, then the rule is that it must be inexpensive (about $10.00 and no more than $20.00) and ideally presented after the semester ends.
Gift Certificate for Coffee
A gift certificate to your professor's favorite coffee shop will be appreciated. Remember to keep the amount small.
Avoid Homemade Baked Goods
Some students present professors with home baked cookies or cakes, but home baked goods are not a good idea. Professors may have allergies to nuts or other common ingredients. More important, many professors make it a habit to not eat homemade edibles from students for safety reasons.
If you'd like to offer a professor with an edible treat, make it a store-bought and wrapped treat, such as chocolates from specialty chocolate store, a tin of assorted teas, or fancy coffees.
Fancy Office Supplies
Binder clips, notebooks, sticky note pads -- these are the tools of academia. Present professors with fancy decorative versions of these basic tools. They're both useful and thoughtful. Holding together papers with a decorative binder clip or writing a note on a pretty sticky note can make daily tasks a little more fun.

